Kundu S K, Chaudhuri B K, Seed A, Jákli A
Solid State Physics Department, Indian Association for the Cultivation of Science, Calcutta-700032, India.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Apr;67(4 Pt 1):041704. doi: 10.1103/PhysRevE.67.041704. Epub 2003 Apr 14.
The temperature and frequency dependent dielectric relaxation behavior of a liquid crystalline (S)-(+)-1-methylheptyl 4-[2-(4-alkoxyphenyl) thiophene-5-carbonylthiooxy] benzoate system is reported. Interesting successive antiferroelectric-ferroelectric-antiferroelectric (AF-FE-AF) phase transitions are observed in this system resembling the successive phase transitions observed in crystalline Rochelle salt. The smectic-C* (SmC*) to AF1 phase transition (around 103.0 degrees C) is first order in nature, predicted from the use of Orihara and Ishibashi theory. It is also found that a contribution of the ferroelectric SmC* phase ordering penetrates even in the antiferroelectric AF1 (SmC()(A)) and AF2 (SmC()(A)) phases very close to the SmC*-AF1 and SmC*-AF2 phase boundaries (critical regions). It is suggested that this type of mixing of AF and FE phases might cause surface induced ferroelectric- or ferroelectric-type ordering near the AF-FE phase transitions. A soft mode with Debye-type dispersion was observed in the SmA phase. The thermal behaviors of dielectric dispersion, absorption, and dielectric strength in different phases are also reported and discussed.
报道了一种液晶（S）-（+）-1-甲基庚基4-[2-（4-烷氧基苯基）噻吩-5-羰基硫氧基]苯甲酸酯体系的温度和频率依赖性介电弛豫行为。在该体系中观察到了有趣的连续反铁电-铁电-反铁电（AF-FE-AF）相变，类似于在结晶罗谢尔盐中观察到的连续相变。根据大原和石桥理论预测，近晶C*（SmC*）到AF1相的转变（约103.0℃）本质上是一级相变。还发现，即使在非常接近SmC*-AF1和SmC*-AF2相界（临界区域）的反铁电AF1（SmC*（A））和AF2（SmC*（A））相中，铁电SmC*相有序化的贡献也会渗透。有人认为，这种AF相和FE相的混合可能会在AF-FE相变附近引起表面诱导的铁电或铁电型有序化。在SmA相中观察到了具有德拜型色散的软模。还报道并讨论了不同相中介电色散、吸收和介电强度的热行为。
